This invention relates in general to electrography and apparatus for fusing toner images carried by supports through the application of heat and pressure. More particularly this invention relates to fuser apparatus including a heated fusing member in which the temperature of said fuser member in a fusing region is maintained substantially uniform along the length thereof.
In the electrographic process, a toner image of fusible particles corresponding to an original is formed on a support such as a copy sheet. The toner image is permanently fixed to the support by means of fuser apparatus including a fuser member, such as a fuser roller or belt, which contacts a support carrying a toner image to fuse the toner image to the support by means of heat and pressure. The fusing surface of the fuser member is preferably formed of a material, such as silicone elastomer, exhibiting good release characteristics and exhibiting resistance to degradation at high temperatures. The fuser roller may be heated by an internal heat source such as a quartz lamp positioned within the roller. It has been found that the temperature distribution across the length of the fuser roller at its fusing surface is generally nonuniform in the fusing region of the roller. This nonuniformity is a function of fuser lamp length, the pattern of heat radiation distribution along the length of the lamp, loss of heat to the bearings and structural members which support the fuser roller, nonuniform heat conductance through the fuser roller due to lenth of supports being fused, etc.
In reproduction machines in which heat-sensitive copy sheets are developed, it has been proposed to provide and maintain a uniform temperature across the outer surface of a heated cylinder. Thus in U.S. Pat. No. 4,064,933 issued Dec. 27, 1977 for "Developing Roller Apparatus For Reproduction Machines", patentee G. A. Schuman, a heated developing roller is disclosed which includes a hollow thin-walled heat conducting rotatable cylinder having relatively small diameter heat pipes mounted on or embedded in its inner wall and extending substantially between the ends of the cylinder. Such a cylinder is disadvantageous due to the complexity and expense of manufacturing a cylinder with the heat pipe integral with or welded to the internal surface thereof. In U.S. Pat. No. 3,952,798, issued Apr. 27, 1976, for "Internally Heated Heat Pipe Roller," patentees D. L. Jacobson et al., there is disclosed a heat pipe which is used as a fusing roller for affixing a powdered image to a support surface or as a device for heating the fusing roller. The disclosed heat pipe is internally heated and presents difficulties in manufacture and complexity in structure. U.S. Pat. No. 4,284,875 issued Aug. 18, 1981, for "Heat Roller Fixing Apparatus," patentees R. Namiki et al, also discloses a complex internally heated heat pipe which may be used as a fixing apparatus in a copier.
It would thus be desirable to provide fuser apparatus having a heated fusing member where the temperature across the length of the fusing member in its fusing region is substantially uniform while at the same time providing a simple, efficient and inexpensive assembly for effecting such uniformity. Improvement in temperature uniformity will be helpful in improving the life of an elastomeric fuser roller and in increasing the range of temperatures over which fusing may be effected.